Sha'Carri Richardson, the US champion and second-fastest 100 metres sprinter in the world this year, will not contest the event at the Tokyo Olympics after receiving a one-month ban for cannabis use.
The positive test means her victory at the US Olympic trials last month has been wiped out, leaving her ineligible for the 100m at the Tokyo Games. There remains a chance she could still be selected for the 4x100m relay.
Richardson, 21, has burst onto the international stage this year, quickly establishing herself as a potential gold medal contender after running a personal best 10.72 seconds in April.
Speaking on Friday, Richardson - who was raised by her grandmother - said she used cannabis after finding out her biological mother had died a few days before the US trials.
Cannabis is legal in Oregon, where the competition took place, but the substance is banned in professional athletics under anti-doping rules.